Communicating with the instrumented end of a drill string inside a well bore deep within the Earth presents unique challenges. The development of real time communications for use in well bores has revolutionized the drilling industry; this is especially evident in measurement-while-drilling (MWD) technologies. Various wireless communication methods have been developed for MWD operations including mud pulse telemetry as well as electromagnetic-based systems. In traditional mud pulse systems, an orifice works in concert with a reciprocating piston to vary the drilling mud pressure near the bottom end of the drill string, thereby forming pulses that transmit through the mud to the surface. Using this system, digitally encoded messages can be sent via mud pulses, said pulses being received and interpreted by telemetry devices located at the surface. In some designs, the orifice represents the bore terminus of the tool string since previous designs have the orifice permanently fixed in position. As a result, it has been previously impossible to pass tools beyond this point, without first removing the entire drill string, a costly and time consuming task. Another design is presented in U.S. Pat. No. 4,636,995 where a flow constrictor and throttling member is provided as an integrated retrievable unit. The unit, however, cannot be displaced and moved downwards past its terminal seat or stop. In addition, the unit positions the pulser unit at the top of the assembly, subjecting the mechanics of the mud pulser to the extreme flow turbulence that is experienced during drilling operations. Additionally, this prior art design does not incorporate a retainer.
There is therefore a significant need for an alternate mud pulse telemetry system that does not obstruct passage of sensing devices through the drill string. A means to remove the obstruction, and an object of the present invention, is to have a mud pulse orifice incorporated into the removable mud pulse generator. This eliminates the obstruction and the limitation of previous mud pulse telemetry systems. A further object is to provide a retainer system in a mud pulse landing assembly that engages the removable mud pulse generator to prevent spatial and rotational movement. Another object is to provide a modular mud pulse generator system that allows for replacement of only those parts that have failed. A removable system must have the ability to self align, should be self-seating and be removable in either the upward or downward direction from the normal operating position.